A conventional stacking apparatus 10 is illustrated in FIG. 8. The stacking apparatus 10 is configured for use adjacent to a rotary die cut machine 12 which cuts blanks (not illustrated) from sheets of material, for example, corrugated paperboard. The stacking apparatus 10 includes a receiving or “layboy” section 14 that receives the blanks from the die cut machine 12 and discharges them onto a transfer conveyor 16. The transfer conveyor 16 carries the blanks to an inclined main conveyor 18, and the blanks travel along the main conveyor 18 to its downstream end 20 where they are discharged into a hopper 22.
After the blanks are discharged from the downstream end 20 of the stacker, they impact a backstop 24 and fall onto a receiving conveyor 26 mounted on a lift table 28. As the stack 30 on the lift table 28 grows, the lift table 28 drops, either continuously or periodically, so that the sheets are always falling approximately the same distance from the downstream end 20 of the stacking apparatus 10 onto the lift table 28 or onto the partial stack 30 on the lift table 28. Alternately, the stack may fall onto a fixed-height conveyor and the end of the main conveyor may rise to maintain a constant distance from the top of the stack.
When the stack 30 has reached a desired height, the lift table 28 lowers the stack 30 to a level even with a secondary conveyor (not illustrated), and the receiving conveyor 26 moves the finished stack 30 away from the stacking apparatus 10. When the stack 30 has moved off the receiving conveyor 26, the lift table 28 raises the receiving conveyor 26 to a level for receiving additional sheets from the downstream end 20 of the stacking apparatus 10.
The rotary die cut machine 12 operates substantially continuously, and sheets of material therefore continue to traverse the stacking apparatus 10 and reach the hopper 22 even while a finished stack is being removed from the receiving conveyor 26. During the time that the receiving conveyor 26 is out of position, accumulator shelves 32 are extended to receive sheets as they leave the downstream end 20 of the main conveyor 18. When the receiving conveyor 26 has discharged a completed stack and returned to a position at the downstream end 20 of the main conveyor 18, the accumulator shelves 32 retract and drop the sheets that have accumulated thereon onto the receiving conveyor 26. Additional sheets exiting the downstream end 20 of the stacking conveyor fall onto the stack, and the process repeats until the stack on the receiving conveyor reaches a desired height.